<p>In <a href="https://github.com/mlpack/mlpack/pull/696#discussion_r67194489">src/mlpack/methods/edge_boxes/feature_extraction_impl.hpp</a>:</p>
<pre style='color:#555'>&gt; +    
&gt; +    this-&gt;Gradient(OutImage, Magnitude, Orientation);
&gt; +    
&gt; +    size_t downscale = std::max(1, (int)(shrink * scale));
&gt; +    
&gt; +    CubeType Hist = this-&gt;Histogram(Magnitude, Orientation,
&gt; +                                downscale, 0);
&gt; +
&gt; +    channels.slice(slice_idx) =
&gt; +    bilinearInterpolation( Magnitude, rsize, csize);
&gt; +    slice_idx++;
&gt; +    for(size_t i = 0; i &lt; InImage.n_slices; ++i)
&gt; +      channels.slice(i + slice_idx) =
&gt; +      bilinearInterpolation( Magnitude, rsize, csize);    
&gt; +    slice_idx += 3;
&gt; +    scale += 0.5;
</pre>
<p>I would recommend to use <code>slice_idx += n_slices</code>instead of <code>slice_idx += 3;</code> there is no guarantee that we call the function with a 3 channel image.</p>

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